Light waveguide data communications (also referred to here as optical data communications) is becoming increasingly popular due to its advantages in relation to systems that use conductive wires for transmission. Such advantages include resistance against radio frequency interference and higher data rates. An example of a light waveguide transmission system is an optical fiber cable link. Such links are widely used for high speed communications between computer systems. Each system that is attached to the link has a transmitter portion and a receiver portion. The transmitter portion includes electronic circuitry that controls a light source such as a laser, to generate a light signal in the cable that is modulated with information and/or data to be transmitted. The light signal is detected at the receiver portion by a light detector, such as a photodiode, and with the help of appropriate circuitry the received data is then demodulated and recovered.
More recently, pluggable transceiver modules have been developed that can connect the host system board of a data communications network device to other network equipment, via an optical link. The module is powered by the host power supply. One side of the module communicates with an application specific integrated circuit (ASIC) of the host, while the other side has communication signal light sources and detectors that are coupled to an optical waveguide that makes up the optical link. Typically, the link between the ASIC and the transceiver module is a serial electrical link. The transceiver module includes transceiver circuitry, namely a transmitter signal conditioner that translates a serial electrical signal from the ASIC to a driver signal that is fed to drive the communications light source, which may include a laser diode. In addition, there is receiver circuitry which includes a light detector (e.g., a photodiode) that converts the communications light signal from the optical link into an electrical signal, followed by a receiver signal conditioner that further translates the output of the light detector into a serial data communications signal that is directed to the ASIC.
In addition to the basic transmitter and receiver circuitry described above, a modern optical transceiver module also has a capability of managing the operation of the module, including stabilizing the laser diode for operation within tight tolerance bands, for high performance. This is because the operating wavelength of the laser diode can vary greatly as a function of temperature. Accordingly, feedback control systems have been implemented in such transceiver modules, to stabilize the operating temperature of the laser diode, for more reliable data transmission. To achieve precise control of the temperature, an active heat pump, such as a thermoelectric cooler (TEC), has been integrated with an externally modulated laser (EML) component of the transceiver. A closed loop control system in the module monitors the temperature of the EML and regulates it, by suitably controlling the thermo electric cooler to provide the needed heating or cooling effect. This is used to quickly bring the laser diode up to temperature upon startup of the module, and to regulate the temperature within a tight tolerance band during module operation.
In addition to the challenges above, manufacturers of optical transceiver modules may wish to comply with an industry standard agreement that specifies a maximum current that can be provided to the module by the host. The control system in the module thus needs to ensure that the maximum power supply current that has been specified is not exceeded during operation.